The present invention relates generally to speakers and, more particularly, to a low-profile piezoelectric speaker assembly suitable for use as an ear speaker in a mobile phone.
Advances in communication and manufacturing technologies have resulted in mobile devices, such as mobile telephones and personal digital assistants, becoming increasingly smaller in size. In particular, mobile phone manufacturers are striving to reduce the thickness of their devices in response to consumer demands. One consequence of these size reductions is that less space is available for speakers and other components. While users prefer mobile devices with small form factors, consumers still expect high quality audio output from their mobile devices. Therefore, there is great interest among manufacturers in finding ways to reduce the size of speakers while maintaining high quality audio output.
The problem of limited space is especially acute with respect to ear speakers in an ultra-thin, “clam-shell” phone design because the overall thickness of the phone (in its closed position) is typically divided between an upper housing, which includes the ear speaker and, in many cases, an LCD display, and a lower housing, which includes a keypad and battery. The overall thickness of the closed phone may be less than 12 millimeters—thus, an ear speaker assembly having a thickness of 1 to 2 millimeters, or even less, is highly desirable.
Ceramic piezoelectric speakers are therefore increasingly being investigated as alternatives to traditional dynamic speakers. In addition to being thinner, ceramic piezoelectric speakers are generally less sensitive to the acoustic cavity in which they are placed. However, using conventional approaches, it is difficult to achieve enough response at low frequencies to meet acoustic requirements for mobile phone applications with ceramic piezoelectric speakers.